For evidence that ramp meters improve traffic flow, one needs only to look to Minnesota. That state pioneered the strategy to increase highway capacity by using signal lights to restrict traffic merging onto a freeway.

To test the effectiveness of ramp meters, the Legislature suspended their use in Minneapolis and St. Paul in 2000. The verdict was clear: Rush-hour crashes jumped 26 percent, and commuting time rose 22 percent, according to a study by Cambridge Systematics.

"Travel time reliability and crashes were all negatively impacted when they shut them down,'' said engineer Laurence Lambert of Stantec Consulting in Baton Rouge. "They immediately saw a degradation in their highway system.''

Now Lambert is principal designer for a project to position seven ramp meters along the Pontchartrain Expressway and Earhart Boulevard in New Orleans. When construction begins this fall, the city will become the latest metropolitan area in the country and the second in Louisiana to deploy the signals to relieve gridlock. The work along the U.S. 90-Pontchartrain Expressway corridor also will include restriping the road to restore a third lakebound travel lane and construction of a flyover ramp at Claiborne Avenue.

Lambert predicts drive times will shorten, crashes will decline and the road's capacity will increase, as demonstrated by research from around the United States. In Seattle, rear-end and sideswipe collisions dropped 30 percent after ramp meters were introduced. Madison, Wisc., saw a 50 percent decrease in wrecks and an improved response to crash scenes.

"Across the country, you see an average 30 percent reduction in crashes,'' Lambert said. "In every instance, you see reductions in travel time and a more reliable corridor day to day.''

An initial study last year found some improvement, but Sherif Ishak, a civil engineering professor at Louisiana State University, recommended further analysis. Engineers were unable to validate the devices' effect on one segment because of a continuing road-widening project. Another evaluation is underway to determine strategies that could further improve efficiency, Ishak said.

"What we can say is there will be some days when there is congestion, but it is manageable with ramp meters. Some days will be heavy and the ramp meters will not be effective,'' Ishak said, referring to conditions such as crashes and inclement weather. "The concept of ramp meters is an active management strategy.''

The change slashed wrecks in the area to almost zero, transportation officials have said. But the new pattern caused cars to stack up on the lakebound expressway in the afternoon, backing them up across the Crescent City Connection onto the West Bank Expressway. Those drivers are stymied by traffic from downtown and the Port of New Orleans merging onto the Pontchartrain Expressway.

For the ramp meter project, engineers will use a fixed-time system, in which the meters will be activated from 6:30 a.m. to 9 a.m. and 3 p.m. to 7 p.m. They will be erected lakebound on Annunciation Street at Baronne Street, Loyola Avenue and Claiborne Avenue and riverbound on the Earhart Expressway at Baronne and Magazine streets.

Signs will warn drivers when the ramp meters are on and instruct cars where to stop. When the signal flashes red, a stop bar will restrict traffic from moving forward. Lambert said the stop delay likely will last less than a minute.

That might seem to increase congestion at ground level, for the sake of easing congestion on the elevated expressway. But Lambert said it actually improves traffic.

"We have video of traffic spilling down the ramps onto the surface street. When they are crawling up the ramps, they are spending more than a minute on the ramps just to get up to another crawling situation,'' he said. "It is a little counterintuitive. The ramp meters' sole function is to break up the group of cars.''

Once the ramp light flashes green, one car may merge onto the expressway, Lambert said. The design will allow cars to move at 4 to 6 second intervals.

If traffic queues on the ramps and feeder streets, the system automatically shuts off. "We are not making the freeway better at the expense of the ramps,'' Lambert said. "The theory is if the mainline is breaking down or the ramp meters can't keep up with demand, they will go dark. They will turn off.''

That is called flushing the system. And that is when the devices won't be effective.

"There will be situations where drivers will be frustrated. They will have to wait to merge onto the freeway and see congestion,'' Ishak said. "They will think it's a useless system.''

Lambert said the ramp meters, restriping and a Claiborne flyover will reduce travel time more than 60 percent, from 37 minutes to 14 minutes in the morning and from 33 minutes to 12 minutes in the afternoon. "The travel times were measured in a micro-simulation model from the crest of the CCC bridge to the westbound merge point of I-10,'' Lambert said.

The $3 million cost will be shared between the state transportation department and Regional Planning Commission. The $1 million restriping project qualifies for federal funding.

Ishak warned that ramp meters are not a "magic'' solution, stressing the system is not designed to eliminate congestion, just to ease it. And the devices have limitations.

In Minnesota, some drivers found themselves waiting five, 10 and even as much as 30 minutes at the meters, according a poll conducted by the Star Tribune newspaper in 2000. There were almost 500 meters deployed around the Twin Cities.

"If you have heavy on-ramp volume and you have to flush the system so often, it defeats the purpose of the ramp meters,'' Ishak said. "Traffic conditions will fluctuate. What you can hope for is if they can improve the conditions 20 to 30 percent of the time, that is still an improvement.''

Baton Rouge employs fixed time ramp meters, which operate on a set schedule. But Ishak said there are other strategies that adjust the meters based on demand. There is also coordination of meters, in which the timing is uniform.

"Other advanced systems can sense the demand on the mainline and make adjustments in the ramp metering timing,'' he said. "When volume is low, it lets more vehicles come from the on ramp.''

While metropolitan areas in half of the states use the signals, there is a resistance among motorists to add one more stop to the daily commute, Lambert said. Many drivers see the signal lights as an inconvenience or nuisance.

But the tide could be changing. "What we've seen is traffic is getting so bad in New Orleans and Baton Rouge, the public supports ideas like this because they are tired of sitting in traffic,'' Lambert said. "They do understand traffic is really getting to be unbearable. Any of these solutions people are willing to try.''